1. Field of the Invention
The present invention relates to a method for forming a color image by a plurality of coloring materials, and more particularly to a method for forming a color image of different colors by controlling quantities of coloring materials in each pixel.
2. Description of the Prior Art
In a prior art color printer or color scanner, tonality correction and masking are effected for R, G and B color signals, and quantities of coloring materials (cyan, magenta, yellow, black) to be deposited on a paper are controlled to control reflection optical densities (hereinafter referred to as OD) of the respective coloring materials to form a color image.
In such an apparatus, it is desirable that a very high density area can also be reproduced. However, because of a limitation to the density of the coloring material and a limitation to quantities of coloring materials deposited in one pixel area, only a definite OD value can be actually reproduced on the paper.
In the prior art, when signals having OD values as shown in FIG. 1A are obtained through image processing including tonality correction and masking, that is, when the OD value for cyan exceeds a maximum OD value reproducible by the cyan coloring material, the cyan is reproduced with the maximum reproducible OD value while magenta and yellow are reproduced with the OD values provided by the image processing unit, as shown in FIG. 1B. In accordance with the prior art method, however, a total balance of cyan, magenta and yellow is lost and a hue will change. In the example of FIG. 1, a clear blue color appears as muddy blue.